The present invention relates to an apparatus and method for transmitting commands over a serial link, and more particularly relates the formation and detection of command sequences from serially transmitted binary characters.
In order to transmit data characters across a serial interface, the data characters are converted to transmission codes so that clocking can be recovered and AC coupling is possible. The code also typically provides for special characters outside the data alphabet for functions such as character synchronization, frame delimiters, abort, reset, idle and diagnostics. Transmission codes generally contain no DC and little low frequency content in order to DC isolate the transmission line from the driver and receiver circuitry, to reduce signal distortion on the line, and to assist in error detection.
U.S. Pat. No. 4,486,739, issued Dec. 4, 1984 to Franaszek et al. for "Byte Oriented DC Balanced (0,4) 8B/10B Partitioned Block Transmission Code" and assigned to the assignee of the present invention, discloses a binary code and an encoder circuit which translates an 8 bit byte of information into 10 binary digits for transmission over electromagnetic or optical transmission lines. Special K characters usable for character synchronization, frame delimiters, abort, reset, idle, diagnostics, etc. are generated by the encoder responsive to a control bit referred to as a K bit. Tables I and II show the resultant coding of data characters, and Table III shows the coding of K characters. To maintain DC balance, either an A form or a complementary B form of sub-blocks of data bits may be used according to the running disparity of the characters being transmitted.
U.S. Pat. No. 4,620,311, issued Oct. 28, 1986 to Schouhamer Immink for "Method of Transmitting Information, Encoding Device For Use in the Method, and Decoding Device For Use in the Method," discloses a method for converting n-bit information words into m-bit code words in which an A form of the code word and a B form of the code word are derived from each other by inversion and reversal.
U.S. Pat. No. 4,683,567, issued July 28, 1987 to Green et al. for "Asynchronous Signaling System For Digital Communication Channel," discloses continuously transmitting a selected one of a plurality of unique N-bit digital code words that corresponds to an associated signaling message. Each adjacent N-bits out of two identical back-to-back N-bit words that define the same unique word will not define a different unique word. Rather the N-bit words, called code words, from the back-to-back pair thereof are ordered permutations of the same ordered group of N-bits where one of them is called a primary code word that is identified with the unique word, and the others are called secondary code words.
U.S. Pat. No. 4,698,809, issued Oct. 6, 1987 to Munster for "Method and Apparatus for the Channelized Serial Transmission of Redundantly Encoded Binary Data," discloses a method of redundantly encoding 2.sup.m encoded binary words wherein m&gt;n, as well as circuits for for the encoding and decoding of the encoded binary words The m words exhibit x invariant bits between themselves and the n words and the m-x bits are mapped uniquely to the remaining n-w bits of the binary words.